Colorants pigment attributes

In many applications ultramarine blue is stable to around 400 °C, violet to 280 °C and pink to 220 °C. All have excellent light fastness with a 7-8 rating (full and reduced shades) on the International Blue Wool Scale. Color fade attributed to light exposure or moderate heat is almost always caused by acid attack. Ultramarines react with all acids, and if there is sufficient acid, the pigment is completely decomposed, losing all color, to form silica, sodium and aluminum salts, sulfur, and hydrogen sulfide. Evolution of hydrogen sulfide with acids is a useful test for ultramarine. 

The use of natural pigments for food applications is gaining soil from day to day [95]. Curcumin, betaine, amarathine, anthocyanins and P-carotene are the most common and widely used pigments [95,96], Saffron s coloring properties attributed mainly to water-soluble carotenoids are used for coloring of foods. The stability of these saffron pigments in aqueous... 

The intense blue color of Pmssian Blue is attributed to electron transfer between the [Fe(CN)3] and Fe(Ill) ions. A related pigment called Berlin Green is obtained by oxidation of Pmssian Blue. It is thought that the intense color of this other compound results only if oxidation of the [Fe(CN)3] units is incomplete and some remain as hexakiscyanoferrate(4—). The compound in which only h on(Ill) is present, Fe[Fe(CN)3] [14433-93-3], is brown and is subject to autoreduction processes. 

Mechanical and Chemical Properties. Colorants, especially pigments, can affect the tensile, compressive, elongation, stress, and impact properties of a polymer (5). The colorants can act as an interstitial medium and cause microcracks to form in the polymer colorant matrix. This then leads to degradation of the physical properties of the system. Certain chemicals can attack colorants and there can be a loss of physical properties as well as a loss of the chromatic attributes of the colorant. Colorants should always be evaluated in the resin in which they will be used to check for loss of properties that ate needed for the particular appHcations. 

Typical attributes for evaluating food quality are safety, shelf life, color, taste, flavor, texture, health, and convenience. The level of a quality attribute is determined by levels of physical, microbial, physiological, chemical, and biochemical food processes, product composition, and applied technological conditions. For example, a combination of enzyme-degrading colorants, compositions and concentrations of pigments, and food structure properties contribute to a certain color level perceived by consumers. Depending on the match of expectation and experience, certain attributes will or will not be perceived as quality. ... 

Recrystallization too is attributable to the pigment having a specific solubility in the plastic. As in other media, it is demonstrated primarily in a change of transparency or opacity in transparent colorations and in the depth of shade in white reductions. Lack of recrystallization stability becomes evident for example in the manufacture and processing of pigment-plasticizer pastes and in various polymers at elevated processing temperatures. 

Incorporated in finishes, P.Gr.8 is heat stable up to about 180°C. It is not entirely fast to overcoating. Most systems containing P.Gr.8 will fail to maintain their color value if they are exposed to acids there is a shift towards yellower hues, a phenomenon which is attributed to demetallation of the pigment. 

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